Coronary artery by-pass method

ABSTRACT

A cardiovascular treatment method utilizes an elongate flexible surgical instrument (e.g., catheter) having a distal end. A distal end portion of the instrument is inserted into a vascular system of a patient. A surgical head at the distal end of the instrument is positioned so that the head is disposed adjacent to myocardium tissue of the patient. The head is operated to form a recess in the myocardium tissue. Prior to operating the head to form the recess, a thickness of the myocardium tissue is measured, the recess formed during the operation having a length determined in accordance with the measured thickness of the myocardium tissue. The thickness measurement partially determines the length of the recess. The angle of entry of the recess with respect to the heart wall also partially determines the length of the recess: the greater the angle, the longer the recess can be for a given myocardium thickness.

This application is continuation of Ser. No. 08/893,643 filed Jul. 11,1997, U.S. Pat. No. 5,908,028 which is a division of Ser. No. 08/665,950filed Jun. 19, 1996, U.S. Pat. No. 5,662,124.

BACKGROUND OF THE INVENTION

This invention relates to a method for effectuating a coronary arterybypass.

Coronary arteries frequently become clogged with plaque which at thevery least impairs the efficiency of the heart's pumping action and canlead to heart attack. The conventional treatment for a clogged coronaryartery is a coronary by-pass operation wherein one or more venoussegments are inserted between the aorta and the coronary artery. Theinserted venous segments or transplants by-pass the clogged portion ofthe coronary artery and thus provide for a free or unobstructed flow ofblood to the heart.

Such conventional coronary artery by-pass surgery is expensive,time-consuming, and traumatic to the patient. Hospital stay subsequentto surgery and convalescence are prolonged.

A new coronary artery by-pass technique is disclosed in U.S. Pat. No.5,429,144. That technique utilizes a stent made of a biocompatiblematerial and comprises steps of moving the stent in a collapsedconfiguration through a blood vessel of a patient's vascular system tothe patient's heart, inserting the stent in the patient's myocardium sothat the stent extends at least partially through the myocardium andonly within the myocardium, and upon the disposition of the stent in themyocardium, expanding the stent from the collapsed configuration to asubstantially tubular expanded configuration so that a blood flow pathis formed at least partially through the myocardium.

Pursuant to U.S. Pat. No. 5,429,144, the stent may be disposed in themyocardium so that it extends only partially through the myocardium,from a coronary artery, upstream of a vascular obstruction, or from theleft ventricle of the heart. Alternatively, the stent may extendcompletely through the myocardium to establish a blood flow path fromthe left ventricle to a coronary artery, downstream of a vascularobstruction. In any case, the stent is deployed so that it extends onlywithin the myocardium and does not protrude beyond the heart tissues,either into the left ventricle or into the coronary artery.

Where the stent of U.S. Pat. No. 5,429,144 extends only partiallythrough the myocardium and thus terminates within the cardiac tissues,the stent guides blood directly into the heart tissues and particularlyinto cardiac vesicles which naturally occur in the myocardium. The bloodis naturally distributed from the vesicles into the cardiac tissues andis collected by the veins of the heart. Where the stent terminateswithin the myocardium and extends from a coronary artery, upstream of avascular obstruction, the stent maintains its expanded form duringdiastole, so that blood pumped from the heart is forced into the stentand from thence into the cardiac tissues. Where the stent terminateswithin the myocardium and extends from the left ventricle, the stent maycollapse during systole, under the compressive forces exerted by thecontracting heart muscle. In that case, blood is delivered to themyocardium during diastole: blood flows into the stent from the leftventricle as the ventricle is filling with blood. Alternatively, wherethe stent terminates within the myocardium and extends from the leftventricle, the stent may maintain its expanded form during systole,despite the compressive forces exerted by the contracting heart muscle.In that case, blood is forced into the stent and from thence into thecardiac tissues during heart contraction.

According to U.S. Pat. No. 5,429,144, the coronary bypass method furthercomprises inserting a distal end portion of a catheter into theperforation or recess prior to the ejection of the stent, and sensingpressure on the catheter along the distal end portion, therebydetermining a thickness of the myocardium at the perforation or recess.The stent is cut from a piece of stent material so that the stent has alength corresponding to the sensed or measured thickness of themyocardium at the perforation or recess.

U.S. Pat. No. 5,429,144 describes the use of a drill head duringdiastole to cut a perforation into the myocardium. The synchronizationor coordination of the drilling and stent ejecting steps with heartaction is implementable by computer. Where the stent is disposed in themyocardium so that the stent extends only partially through themyocardium from the patient's left ventricle, the stent is inserted intothe myocardium from the left ventricle. Accordingly, a distal end of thecatheter is passed into the left ventricle prior to the deployment ofthe stent, while the stent is moved in its collapsed configurationthrough the catheter and into the left ventricle of the heart.

OBJECTS OF THE INVENTION

An object of the present invention is to provide an improved method forforming a coronary artery by-pass to thereby enable the oxygenation ofcardiac tissues.

Another object of the present invention is to provide a method forforming a coronary artery by-pass which does not require leaving adevice in the patient.

A further object of the present invention is to provide such a methodwhich is less invasive and less traumatic to the patient thanconventional by-pass surgery.

SUMMARY

Basically, the present invention is directed to a stent-less coronaryartery by-pass wherein one or more recesses are formed in themyocardium. The recesses open sufficiently during diastole to permitblood flow into the myocardium and the vesicles therein.

A cardiovascular treatment method in accordance with the presentinvention utilizes an elongate flexible surgical instrument (e,.g.catheter) having a distal end. A distal end portion of the instrument isinserted into a vascular system of a patient. A surgical head at thedistal end of the instrument is positioned so that the head is disposedadjacent to myocardium tissue of the patient. The head is operated toform a recess in the myocardium tissue. Prior to operating the head toform the recess, a thickness of the myocardium tissue is measured, therecess formed during the operation having a length determined inaccordance with the measured thickness of the myocardium tissue. Thethickness measurement partially determines the length of the recess. Theangle of entry of the recess with respect to the heart wall alsopartially determines the length of the recess: the greater the angle,the longer the recess can be for a given myocardium thickness.

The thickness of the myocardium may be measured by generating anultrasonic pressure wave, sensing reflected pressure waves and analyzingthe reflected pressure waves to determine the thickness. The ultrasonicpressure wave generator (e.g., a piezoelectric crystal) and theultrasonic wave sensor (also a piezoelectric crystal) may be disposed inthe catheter wall at the distal tip thereof, or at the distal tip of anancillary instrument inserted through a lumen of the catheter.

Measuring the thickness of the myocardium may be implemented byoperating a computer aided tomography scanning machine, a magneticresonance imaging machine or an echocardiogram device.

Generally, it is contemplated that the recess terminates in themyocardium tissue and is formed from the left ventricle of the patient.Accordingly, the surgical head is disposed adjacent to an inner side ofthe myocardium tissue, inside the left ventricle, so that the recessextends from the left ventricle.

According to a feature of the present invention, the surgical head is acontact laser tip. In that case, operating the surgical head includestransmitting monochromatic coherent electromagnetic radiation (laserenergy) through the contact laser tip to the myocardium tissue.Alternatively, the surgical head may include a drill tip, the operatingof the head including pushing the drill tip into the myocardium tissueand rotating the drill tip during the step of pushing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a human heart, showing aplurality of recesses formed in the myocardium for providing a pluralityof pathways for guiding blood directly into the cardiac tissues from theleft ventricle, in accordance with the present invention.

FIG. 2 is a partial cross-sectional view, on a larger scale, showing oneof the recesses of FIG. 1.

FIG. 3 is partially a schematic longitudinal cross-sectional view andpartially a block diagram of an instrument assembly for forming therecesses shown in FIG. 1.

FIG. 4 is partially a schematic longitudinal cross-sectional view andpartially a block diagram of another instrument assembly for forming therecesses shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention seeks to oxygenate the cardiac muscle ormyocardium MYO (FIG. 1) where a coronary artery AC is blocked withvascular plaque material VP. To that end, a distal end portion of anangioplastic instrument 12 or 14 (FIGS. 3, 4) is inserted through afemoral artery (not shown) and the aorta AO into the left ventricle VL.More particularly, a distal end of a steerable catheter 16 or 18 (FIGS.3, 4) is inserted along a predetermined path 92, 94, 96 through thevascular system of the patient and into left ventricle VL. Instrument 12or 14 is then operated to form a plurality of recesses 86, 88 and 90 inmyocardium MYO for providing a plurality of pathways for guiding blooddirectly into the cardiac tissues from left ventricle VL. Recesses 86,88, and 90 extend from left ventricle VL and terminate within myocardiumMYO. Each recess 86, 88, and 90 thus extends only partially intomyocardium MYO.

As illustrated in FIG. 3, angioplastic surgical instrument 12 includes apiezoelectric transducer 20 disposed at a distal tip of catheter 16 andelectrically connected to an ultrasonic frequency generator 22. Anotherpiezoelectric transducer 24 disposed at the distal tip of catheter 16 isoperatively coupled to a wave analyzer 26 which serves to determine thethickness of myocardium MYO upon disposition of the distal end ofcatheter 16 inside left ventricle VL. Wave analyzer 26 is connected to adisplay 28 for indicating a computed heart wall thickness to a vascularsurgeon.

As further illustrated in FIG. 3, an optical fiber 30 is insertedthrough a lumen 32 of catheter 16. At a proximal end, fiber 30 extendsto a laser source 34, while at a distal end fiber 30 is provided with asurgical head in the form of a tapered contact tip 36 of conventionalcrystalline material. Tip 36 delivers coherent monochromaticelectromagnetic radiation from laser source 34 to target tissues of thepatient's heart HP (FIG. 1). A position encoder 38 is operatively linkedto fiber 30 for measuring a linear displacement of the fiber during theformation of recesses 86, 88, 90. Encoder 38 is connected to display 28for indicating a measured fiber displacement to a vascular surgeon.

As depicted in FIG. 4, catheter 18 is provided with a pair of lumens 40and 42 which receive an ultrasonic probe 44 and an optical fiber 46,respectively. Ultrasonic probe 44 includes an electroacousticpiezoelectric transducer 48 disposed at a distal tip of the probe andelectrically connected to an ultrasonic frequency generator 50. Anacoustoelectric piezoelectric transducer 52 also disposed at the distaltip of probe 44 is operatively coupled to a wave analyzer 54. Analyzer54 processes reflected ultrasonic wave pressures, sensed by transducer52, to determine the thickness of myocardium MYO (FIG. 1) upondisposition of the distal end of catheter 18 with probe 44 inside leftventricle VL. The results of the thickness computations of analyzer 54are transmitted to a monitor 56 for display.

As additionally depicted in FIG. 4, optical fiber 46 extends at one endto a laser source 58 and is provided at an opposite end with a surgicalhead in the form of a tapered contact tip 60. Tip 60 is made ofconventional crystalline material and functions to deliver coherentmonochromatic electromagnetic radiation from laser source 58 to targettissues of the patient's heart HP (FIG. 1). A position encoder 62 iscoupled to fiber 46 for measuring a linear displacement of the fiberduring the formation of recesses 86, 88, 90. Encoder 62 is connected tomonitor 56 for indicating a measured fiber displacement.

As further shown in FIG. 4, catheter 18 incorporates in its wall aplurality of strain gauges 64 distributed along the catheter. Straingauges 64 are operatively connected to a computer or microprocessor 66which analyzes the signals from the strain gauges to determine theconfiguration of catheter 18 inside the patient. The computedconfiguration is displayed on monitor 56, together with an image ofinternal organs of the patient. The image of the internal organs isproduced, for example, by magnetic resonance imaging (MRI), computeraided tomography (CAT) or an echocardiograph.

Upon insertion of the distal end of catheter 16 or 18 into leftventricle VL and upon the orientation of the catheter tip at apredetermined angle a1 (FIG. 2) with respect to the perpendicular 98 tothe myocardium MYO, an a-c electrical current of ultrasonic frequency istransmitted from generator 22 or 50 to transducer 20 or 48 to produce anultrasonic pressure wave. This pressure wave is reflected from inner andouter surfaces (not designated) of myocardium MY. The reflectedultrasonic pressure waves are sensed by transducer 24 or 52 and analyzedby analyzer 26 or 54 to determine the thickness of myocardium MYO in anarea located immediately in front of the distal end of catheter 16 orprobe 44. Provided with cardiac wall thickness information via display28 or monitor 56, a vascular surgeon can determine an appropriate lengthfor a recess 86, 88, or 90 to be formed in the myocardium. Recesses 86,88, and 90 have a length sufficiently large to effectuate artificialcardiac vascularization but small enough to not traverse the myocardium.

Upon the determination of the entry location, entry angle al and thedepth or length of the recess 86 to be formed, laser fiber 30 or 46(FIGS. 3, 4) is ejected from catheter 16 or 18 and contact tip 36 or 60is placed in contact with the myocardium tissues. Laser energy istransmitted from source 34 or 58 to form recess 86 at angle a1 inmyocardium MYO. Fiber 30 or 46 is advanced a predetermined distance intomyocardium MYO, the distance of penetration of tip 36 or 60 beingascertained by position encoder 38 or 62.

The formation of recesses 86, 88 and 90 as described hereinabove may beimplemented in part via a computer programmed to enable the timing ofheart perforation, catheter insertion, and other operations so thatthose operations are performed only during the diastolic phase of acardiac cycle. The programming and utilization of a computer in such aprocedure will be clear to one skilled in the art from the teachings ofU.S. Pat. No. 4,788,975 to Shturman et al., the disclosure of which ishereby incorporated by reference.

As stated above, it is contemplated that laser energy is transmittedalong fiber 30 or 46 to form recess 86, 88 or 90 only during a diastolicphase of a cardiac cycle. In some cases, tip 36 or 60 may be left inplace in myocardium MYO during a limited number of systolic iterations,to enable completion of recess formation. Alternatively, the contact tip36 or 60 may be removed during systole and reinserted during diastoleuntil the recesses are formed.

After a cardiac vascularization operation as described above iscompleted, blood drains into recesses 86, 88, 90 from left ventricle LVand penetrates to vesicles VCS in the myocardium MYO during diastole.The blood is naturally distributed from vesicles VCS into cardiactissues and is collected by the veins (not shown) of the heart. Eventhough some of the blood may return to ventricle VL during systole (andfrom thence to aorta AO), enough blood remains in the myocardium toprovide adequate oxygen and nutrients thereto.

In addition to one or more recesses 86, 88, and 90 inserted from theleft ventricle VL partially into myocardium MYO, one or more recessesmay be formed to connect left ventricle VL with coronary artery AC, asdescribed in U.S. Pat. No. 5,429,144, the disclosure of which is herebyincorporated by reference. As additionally described in U.S. Pat. No.5,429,144, the formation of recesses 86, 88 and 90 may be implementedwith a rotary drill rather than a contact laser. U.S. Pat. No. 5,429,144also discloses steering componentry which enables an operator tocontrol, from outside the patient, an orientation of the distal tip ofcatheter 16 or 18 upon insertion of the catheter into the patient.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. It is to be noted, for example, that the measurementof cardiac wall thickness may be alternatively accomplished via an MRImachine, a CAT scanner or by an echocardiogram. For example, a“measuring rod” of a predetermined length may be inserted through theangioplastic catheter. A computer connected to a CAT-scanner, an MRImachine or other imaging device then automatically determines myocardiumthickness by comparing the dimensions thereof to the known length of the“measuring rod.” The computer with scanner input may be additionallyused to determine optimal locations and insertion angles of multiplestents, e.g., stents 86, 88, and 90.

Accordingly, it is to be understood that the drawings and descriptionsherein are profferred by way of example to facilitate comprehension ofthe invention and should not be construed to limit the scope thereof.

What is claimed is:
 1. A method for treating a heart, comprising:positioning a distal end of an instrument proximate to a heart wall;measuring a thickness of the heart wall; and forming a recess in theheart wall with the instrument, said recess having a length determinedin accordance with the measured thickness of the heart wall.
 2. Themethod of claim 1, wherein forming the recess includes forming aplurality of recesses in the heart wall.
 3. The method of claim 1,wherein forming the recess includes forming the recess from the leftventricle into the heart wall surrounding the left ventricle.
 4. Themethod of claim 1, wherein measuring the thickness of the heart wallincludes indicating a measurement of the thickness of the heart wallwithout penetrating the heart wall.
 5. The method of claim 1, whereinmeasuring the thickness of the heart wall includes transmitting apressure wave and sensing a reflected pressure wave.
 6. The method ofclaim 1, wherein measuring the thickness includes using one ofcomputer-aided tomography scanning, magnetic resonance imaging, andechocardiogram.
 7. The method of claim 1, wherein forming the recessincludes one of lasing and drilling.
 8. The method of claim 1, whereinforming the recess includes terminating the recess within the heartwall.
 9. The method of claim 1, wherein the positioning includesinserting the instrument into a left ventricle such that the distal endis proximate an interior portion of the heart wall surrounding the leftventricle.